Cook visited the office of the Beijing-based start-up, known for its yellow bikes, and met with founding members including CEO Dai Wei, according to Cook's microblog and ofo.

"Thanks for welcoming me today, ofo team! Great energy behind your mission to make commuting greener, more efficient and fun!" Cook said in his official Sina Weibo post, along with pictures of him riding an ofo bike.

Cook's visit comes amid a fierce contest for users and investors among China's bike-sharing start-ups, which has drawn in large global tech investors. The competition is frequently compared to a similar battle for the ride-sharing market between Uber Technologies [UBER.UL] and local rival Didi Chuxing a year ago.

Ofo, which counts Didi as an investor, said Cook came for a company visit on Tuesday and did not discuss investment or collaboration. It raised $450 million earlier this month and saw its valuation pass the $1 billion mark.

Ofo and its main rival Mobike are among a growing number of bike-sharing services that have sprung up in China that allow users to find, unlock and pay to rent trackable bicycles through smartphone apps. It targets younger consumers seeking to get around congested roads and public transport.

Ofo says it operates in 43 cities in China with 2.2 million bikes. It also claims pilot schemes in Singapore, London and California.

Shanghai-based Mobike, which has raised more than $300 million so far this year from investors including Tencent Holdings <0700.HK>, Warburg Pincus, and Singapore state investor Temasek Holdings, said on Tuesday it was fully launching in Singapore.